The physical geography of Dunhuang, its region, and the approaches to
it help to explain why the town became so important militarily. The most logical route
from the interior of China to the West moves through the "funnel" of the Gansu
or Hexi Corridor, bounded on north and south by mountains. The mountains to the south are
high enough to serve as barriers to invasion, and their glaciers fed the streams which
made habitation in an otherwise dry region possible. To the north, the terrain is less
well defended by nature; it was for this reason that, beginning in the last centuries BCE,
the rulers of China began to create the "Great Wall," to defend against nomadic
incursions. The Han emperors, especially beginning with Wu-Ti (141-87 BCE) extended the
wall and its network of watchtowers along the Hexi corridor, through the
"bottleneck" at Jiayu Guan (later to be the western boundary of China under the
Ming) along both sides of the broadening valley past Anxi and well beyond Dunhuang. The
British explorer Aurel Stein made the exciting discovery that the Han "limes"
extended all the way to Lop Nor, the salt lake at the edge of the Taklamakan Desert.

While it was possible for invaders to break through the defenses to the
east of Dunhuang, the fortifications there in a real sense were the gateway to inner
China. Even at the greatest extent of Chinese power in Inner Asia in the period up to the
end of the first millenium CE, Chinese control beyond Dunhuang was exercised largely
through vassal states. Written records indicate that Chinese travelers to the West clearly
sensed they had stepped into another world at the moment they passed through the
"Jade Gate." To go beyond was to leave behind the comforts of home and to enter
culturally alien lands. Except for the garrisons manning the watch towers and small forts,
Chinese armies almost inevitably retreated behind the defenses, often in disarray from
their inability to provision themselves adequately on long stages through the desert.

The resources invested in maintaining the defenses were substantial and
the wisdom of such expense obviously was much debated at the Chinese court. Han narrative
histories make it clear that the commitment to the defensive lines fluctuated--at times
the walls were allowed to decay, and there was the temptation of agreements with
submissive neighbors to allow them to man the defenses. Hiring of mercenaries seems to
have been quite common; at the same time, the soldiers sent out from the center of the
empire were provided with agricultural land to maintain themselves, although apparently
not always adjacent to where they actually served. The supply of food to the more remote
outposts was through a highly bureaucratized quartermaster corps, whose records have been
unearthed in the ruins of the watchtowers.

The military architects of the fortifications deserve high marks for
their skill and ability to take advantage of the local terrain and building materials.
While our image of the Great Wall derives from those sections built in stone in the
mountains north of Beijing, in the Dunhuang region, the construction material tended to be
pounded earth layered with reed mats or grids to provide stability. The arid conditions
have helped ensure the survival of major sections of the wall, forts and beacon towers.
Sections of the wall retreat into the distance in an absolutely straight line; in general
an effort was made to maximize the strategic advantage provided by naturally occurring
ridges and hills or swamps and rivers. Generally beyond the wall, in "no man's
land," beacon towers commanded heights or passages through the valleys which erosion
had carved through the mountain barrier.

Perhaps the most impressive thing about the physical remains of the
defenses in the Dunhuang region is how extensive they are. Beginning in Anxi, to the east
of Dunhuang and moving to the west and southwest of the city, a distance of some 250 km.,
there are extensive sections of wall, dozens of watchtowers, and many ruins of forts or
supply depots, most apparently dating from Han times. This image map displays the
lines of the Han fortifications (as attested by their remains). For images and some
further explanation regarding individual sections of the defenses, click on various
"live" locations on the map. Quite extensive material has been provided
for the region west of Dunhuang.

For centuries, a significant portion of the traffic between the Chinese
heartland and inner Asia was funneled through Dunhuang. The reign of Emperor Wu-ti marked
the beginning of a campaign of aggressive Han expansion to the West in order to combat the
nomadic Hsiung-nu. The Hexi Corridor came under Han control as a result of battles in 121
and 119 BCE; in 111 BCE a decree established the Dunhuang commandery, whose 2000 soldiers
were establish a military colony and extend the fortifications beyond the city. It seems
clear though that the more distant units on the edge of the desert wastes could not have
been engaged in any significant productive agriculture, given the forbidding natural
conditions. The culmination of these successful military campaigns was a victory by Han
armies as far west as the Ferghana Valley in 101 BCE. By the year 9 CE, a census recorded
some 11,200 households in Dunhuang.

Stein's discovery of documents (mainly written on strips of wood) in
the ruins of the fortifications at the "Jade Gate" (Yumen guan), which
controlled the road to the West, confirms the chronology of Dunhuang's early history, as a
number of them date from the 90s BCE. At the watchtower farthest west along this defensive
line, Stein found records dating from around 60 BCE, precisely the period when other
documentation tells of the establishment of the Han Protectorate General for the Western
Regions and the further extension of the system of military colonization.

Of course, as we know, Han fortunes in the West fluctuated and along
with them the extent of firm military control. Stein determined that in the area around
the "Jade Gate" a secondary line of fortifications came into being during the
period of the usurper Wang Mang (9-23 CE), confirming other evidence to the effect that
during this period of weakness, the Han pulled back from their forward positions further
to the West. This is precisely the period when we know the Hsiung-nu were able to a degree
to reassert their control in areas of the Western Regions. The Han reasserted their
control in the Tarim Basin in the last three decades of the first century CE but again
pulled back, due to fiscal exigencies, beginning in 107. Without attempting here to fill
in additional details of the chronology of the defensive lines in the immediately
succeeding centuries, we would merely point out that the archaeological evidence documents
the continuing traffic through the Jade Gate in the T'ang period.